There has been known a system that assists driving by automatic driving or the like during driving, such as parking of a vehicle. In such a system, the vehicle is controlled based on the turning radius of the vehicle, which is stored in advance in association with the steering angle of a steering unit, such as a steering wheel, in a storage device or the like. See, for example, JP 2010-269707 A (Reference 1).
However, a vehicle may drive with a turning radius different from the turning radius, which is associated in advance with the steering angle based on characteristics of each vehicle, etc. In this case, the turning radius of the running route, on which the vehicle actually drives, may not be estimated with high accuracy.
Thus, a need exists for a driving assist system which is not susceptible to the drawback mentioned above.